PCB is excellent in insulation and fire-resistant so that is used mainly as an insulating oil and a heating medium, for widespread purposes. However, since PCB is very stable chemically, it remains for a long period of time after being discharged into environment, and causes a human a bad influence. Therefore, both of production of PCB and use thereof are forbidden, and one produced in the past is kept under sealing. PCB and secondary products using it are kept so much in a depository. If PCB is kept in a long period of time, the PCB has risk of flowing out by obsolescence of the depository. So a processing for making PCB nontoxic is desired strongly.
Since it is hard to decompose, the processing for making PCB nontoxic is very difficult. But various processing methods are examined. For instance, a decomposing method of PCB by microbes is mentioned in Japanese Patent Provisional Publication No. 4-370097, and a chemical decomposing method of PCB is mentioned in Japanese Patent Provisional Publication No. 8-141107. Moreover, there is also a decomposing method of PCB by burning at high temperature.
However, these former decomposing methods of PCB have certain technical or economical problems. For instance, it is unsuitable for a mass processing since a processing speed is slow, or toxic substance is included in exhaust gas after the processing, or equipment thereof is very expensive.
Especially, since PCB comprises chlorine in molecular structure, dioxin is produced in decomposition reaction of PCB secondarily. It is well known that dioxin has toxicity, carcinogenicity and residual property. Therefore, it is considered that the processing which dioxin is contained in exhaust gas has a fatal defect.
On the other hand, an effective method for decomposing and removing dioxin is mentioned in Japanese Patent Provisional Publication No. 2002-35772 which was applied by applicants of this patent.
In the present invention, PCB is decomposed to completely nontoxic substance using the technique mentioned in Japanese Patent Provisional Publication No. 2002-35772. It is an object of the present invention to provide a processing method and equipment for PCB, which uses the simple equipment and is suitable for a quick mass processing at a low cost, and which exhaust gas emitted into atmosphere and residue dumped into natural environment are safe.